My service engine light comes on for a couple weeks at a time and goes off for a couple of weeks at a time. I had the code read at auto zone ant it said a large emission leak (p 4045 i believe) so i replaced the gas cap to no avail. I do not understand why the light comes on and off so regularly if there is a problem. I would think it would just stay on. I just had an oxygen sensor replace less than a year ago for the same light for about $800. Do I really need to get this looked at or is there anything I can check myself?